Organic electroluminescence device

ABSTRACT

The invention is an organic electroluminescent device that comprises organic compound layer(s) including at least one organic emitting layer sandwiched between a pair of electrodes, wherein at least one organic compound layer is formed from an organic compound material having an impurity concentration of lower than 1000 ppm. The device has the advantages of applicability to lightweight, thin and low-voltage driving displays, good luminescent capacity attenuating little even in long-term driving operation, and good durability.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent device(hereinafter this will be referred to as an organic EL device) . Moreprecisely, the invention relates to an organic EL device having theadvantages of applicability to lightweight, thin and low-voltage drivingdisplays, good luminescent capacity attenuating little even in long-termdriving operation, and good durability.

BACKGROUND ART

As being self-luminescent, organic electroluminescent, EL devices havehigh visibility. In addition, they have high impact resistance as beingcompletely solid devices. Therefore, they are much used in variousfields of thin-film display devices, back lights for liquid-crystaldisplays, flat light sources, etc.

Distributed electroluminescent devices are now in practical use. As theyrequire alternating voltage of at least tens volts and 10 kHz or more,their driving circuits are complicated.

In the circumstances, organic EL devices capable of being driven atlowered voltage of 10 volts or so and capable of emitting high-luminancelight are much studied these days. For example, thin-film organic ELdevices having a multi-layered structure of transparent electrode/holeinjection layer/emitting layer/back electrode are proposed in Appl.Phys. Lett., Vol. 51, pp. 913-915 (1987) by C. W. Tang and S.A. VanSlyke, and in Japanese Patent Laid-Open No. 264629/1988. These are sodesigned that the hole injection layer therein can efficiently injectholes into the emitting layer therein. The emitting layer in suchorganic EL devices may have a single-layered structure, which, however,could not enjoy well-balanced electron transportation and holetransportation. To solve the problem, the emitting layer is modified tohave a multi-layered structure of improved performance.

However, the process of forming the multi-layered emitting layer iscomplicated and takes a lot of time. Another problem with it is that themulti-layered structure is against the recent tendency in the art whichis toward reducing the thickness of layers constituting organic ELdevices. On the other hand, down-sized, compact and portable informationappliances are much desired these days, and they are required to bedriven at low voltage. In the circumstances, various types oflight-emitting materials and hole-transporting materials are tried forsuch lightweight, low-voltage driving appliances.

Further, the most important theme in practical studies of organic ELdevices is to establish the technique of preventing the attenuation ofthe luminance of the devices in long-term driving and to providepracticable organic EL devices. In this respect, it is said that thepurity of organic compounds to be used for producing constituentmaterials for organic EL devices has a great influence on theattenuation of the luminous efficiency and the luminance of the devicesproduced, for example, as in “Monthly Display, Sept. 15, 1995”, and“Applied Physics, Vol. 66, No. 2, pp. 114-115, 1997”. However, theinfluences of the structures and the properties of organic compounds tobe used for producing organic EL devices on the properties of thedevices produced are not as yet clarified, and no method has heretoforebeen established capable of quantitatively determining the influences inquestion.

In that situation, the object of the present invention is to provide anorganic EL device having the advantages of applicability to lightweight,thin and low-voltage driving displays, good luminescent capacityattenuating little even in long-term driving operation, and gooddurability.

DISCLOSURE OF THE INVENTION

We, the present inventors have assiduously studied in order to attainthe object as above, and, as a result, have found that the object can beattained by an organic EL device in which at least one organic compoundlayer comprises an organic compound material having an impurityconcentration of smaller than 1000 ppm including 0 ppm. On the basis ofthis finding, we have completed the present invention.

Specifically, the invention is summarized as follows:

(1) An organic electroluminescent device that comprises organic compoundlayer(s) including at least one organic emitting layer sandwichedbetween a pair of electrodes, wherein at least one organic compoundlayer is formed from an organic compound material having an impurityconcentration of lower than 1000 ppm.

(2) An organic electroluminescent device that comprises organic compoundlayer(s) including at least one organic emitting layer sandwichedbetween a pair of electrodes, wherein at least one organic compoundlayer is formed from an organic compound material having an impurityconcentration of lower than 500 ppm and the impurity therein is ahalogen-containing compound.

(3) The organic electroluminescent device of above (2), wherein thehalogen-containing compound is a halogen compound.

(4) The organic electroluminescent device of any of above (1) to (3),wherein the organic compound layers are a hole injection layer, anorganic emitting layer and an electron injection layer.

(5) The organic electroluminescent device of any of above (1) to (4),wherein at least one organic compound material to form the organiccompound layer(s) is purified through sublimation.

(6) The organic electroluminescent device of any of above (1) to (4),wherein at least one organic compound material to form the organiccompound layer(s) is purified through recrystallization orreprecipitation, or through recrystallization combined withreprecipitation.

(7) A method for selecting organic compound materials for organicelectroluminescent devices, comprising determining, throughhigh-performance liquid chromatography, the impurity content of eachorganic compound material to form organic compound layers for thedevices, selecting those having an impurity content of smaller than 1000ppm out of the materials analyzed, and using the thus-selected materialsfor forming the organic compound layers.

(8) A method for selecting organic compound materials for organicelectroluminescent devices, comprising determining the impurity contentof at least one organic compound material to form organic compoundlayers for the devices, selecting those having an impurity content ofsmaller than 1000 ppm out of the materials analyzed, and using thethus-selected materials for forming the organic compound layers.

(9) The method of above (7) or (8) for selecting organic compoundmaterials for organic electroluminescent devices, wherein the impurityin the organic compound materials is a halogen-containing compound.

BEST MODES OF CARRYING OUT THE INVENTION

Modes of carrying out the invention are described hereinunder.

The invention is an organic EL device that comprises organic compoundlayer (s) including at least one organic emitting layer sandwichedbetween a pair of electrodes, wherein at least one organic compoundlayer is formed from an organic compound material having an impurityconcentration of lower than 1000 ppm (by weight, but, as the case maybe, by volume).

The organic EL device of the invention comprises organic compoundlayer(s) including at least one organic emitting layer sandwichedbetween a pair of electrodes. Its typical structures are mentionedbelow, but are not limitative.

<1> Anode/emitting layer/cathode

<2> Anode/hole injection layer/emitting layer/cathode

<3> Anode/emitting layer/electron injection layer/cathode

<4> Anode/hole injection layer/emitting layer/electron injectionlayer/cathode

<5> Anode/organic semiconductor layer/emitting layer/cathode

<6> Anode/organic semiconductor layer/electron barrier layer/emittinglayer/cathode

<7> Anode/organic semiconductor layer/emitting layer/adhesion improvinglayer/cathode

<8> Anode/hole injection layer/hole transporting layer/emittinglayer/electron injection layer/cathode

The organic EL device of the invention may have any of these layerstructures, but preferably has the layer structure <8>. The organiccompound layers referred to herein include the emitting layers andothers sandwiched between the anode and the cathode in the layerstructures mentioned above. In the organic EL device of the invention,at least any one of these organic compound layers is formed from anorganic compound material having an impurity concentration of lower than1000 ppm.

The organic EL device is formed on a transparent substrate. Thetransparent substrate supports the organic EL device, and itstransparency in a visible ray range of from 400 to 700 nm is preferablyat least 50%. Also preferably, the substrate is flat and has a smoothsurface.

Preferred examples of the transparent substrate of that type are glassplates, synthetic resin plates, etc. The glass plates may be made of,for example, soda-lime glass, barium-strontium glass, lead glass,aluminosilicate glass, borosilicate glass, barium borosilicate glass,quartz, etc. The synthetic resin plates may be made of, for example,polycarbonate resins, acrylic resins, polyethylene terephthalate resins,polyether sulfide resins, polysulfone resins, etc.

For the electrode material for the anode, preferred are metals, alloys,electroconductive materials and their mixtures having a large workfunction (at least 4 eV). Specific examples of the electrode materialare metals such as Au, etc.; and electroconductive materials such asCuI, ITO, SnO₂, ZnO, etc. To form the anode, the electrode material isformed into a thin film through vapor deposition, sputtering or thelike. For its properties, it is desirable that the anode through whichthe light from the emitting layer is taken out has a light transmittanceof larger than 10%. Also preferably, the sheet resistance of the anodeis at most hundreds Q/square. Though depending on its material, theanode has a thickness generally falling between 10 nm and 1 μm, butpreferably between 10 nm and 200 nm.

It is desirable that the emitting layer in the organic EL device of theinvention has all the following functions.

<1> Hole and electron receiving function: This is to receive holes fromanodes and hole injection layers and receive electrons from cathodes andelectron injection layers while in an electric field.

<2> Hole and electron transporting function: This is to move theinjected charges (electrons and holes) by the force of the electricfield.

<3> Light emitting function: This is to provide a site for electron-holerecombination to emit light.

In the anode, the degree of hole injection may differ from that ofelectron injection, and the degree of hole transportation and that ofelectron transportation that are represented by hole and electronmobility may also differ from each other. Preferably, any one type ofthe charges is moved in the anode.

The light-emitting material in the organic EL device is principally anorganic compound. Concretely, it includes the following compounds, anyof which are used in the device depending on the desired color tone.

For example, for UV to violet emission, compounds of the followinggeneral formula [1] are preferred.

wherein X represents a group of the following general formula [2]:

and Y represents a group of the following general formula [3]:

For the phenyl, phenylene and naphthyl groups in the compounds offormula [1], usable are compounds having one or more substituents suchas an alkyl group having from 1 to 4 carbon atoms, an alkoxy grouphaving from 1 to 4 carbon atoms, a hydroxyl group, a sulfonyl group, acarbonyl group, an amino group, a dimethylamino group, a diphenylaminogroup, etc. A plurality of these substituents, if any, may be bonded toeach other to form a saturated 5-membered or 6-membered ring. Regardingtheir configuration, the phenyl, phenylene and naphthylene groups in thecompounds are preferably para-positioned, since the bonding stability isgood and since the compounds can be easily formed into flat and smoothfilms through vapor deposition. Specific examples of the compounds offormula [1] are mentioned below.

Of these compounds, especially preferred are p-quaterphenyl derivativesand p-quinquephenyl derivatives.

For blue to green emission, for example, employable arebenzothiazole-type, benzimidazole-type, benzoxazole-type and otherfluorescent brightening compounds, metal-chelated oxinoide compounds andstyrylbenzene compounds. For these, for example, referred to are thecompounds described Japanese Patent Laid-Open No. 194393/1984. Stillother compounds usable herein are listed in Chemistry of Synthetic Dyes,1971, pp. 628-637, and 640.

For the chelated oxinoide compounds, for example, usable are thecompounds described in Japanese Patent Laid-Open No. 295695/1988.Typically, preferred are 8-hydroxyquinoline metal complexes such astris(8-quinolinol)aluminium, etc., and also dilithiumepinetridione, etc.

For the styrylbenzene compounds, for example, usable are the compoundsdescribed in European Patents 0319881 and 0373582. Also usable for thematerial for the emitting layer are distyrylpyrazine derivatives such asthose described in Japanese Patent Laid-Open No. 252793/1990. Apart fromthese, still usable for the material for the emitting layer arepolyphenyl compounds such as those described in European Patent 0387715.

In addition to the fluorescent brightening agents, metal-chelatedoxinoide compounds, styrylbenzene compounds and others mentioned above,further usable for the material for the emitting layer are, for example,12-phthaloperinone (in J. Appl. Phys., Vol. 27, L 713, 1988),1,4-diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene (both inAppl. Phys. Lett., Vol. 56, L 799, 1990), naphthalimide derivatives (inJapanese Patent Laid-Open No. 305886/1990), perylene derivatives (inJapanese Patent Laid-Open No. 189890/1990), oxadiazole derivatives (inJapanese Patent Laid-Open No. 216791/1990, or the oxadiazole derivativesdisclosed by Hamada et al. in the 38th Applied Physics-related JointLecture Meeting), aldazine derivatives (in Japanese Patent Laid-Open No.220393/1990) pyrazoline derivatives (in Japanese Patent Laid-Open No.220394/1990), cyclopentadiene derivatives (in Japanese Patent Laid-OpenNo. 289675/1990), pyrrolopyrole derivatives (in Japanese PatentLaid-Open No. 296891/1990), styrylamine derivatives (Appl. Phys. Lett.,Vol. 56, L 799, 1990), coumarin compounds (in Japanese Patent Laid-OpenNo. 191694/1990), polymer compounds such as those described inInternational Patent Publication WO90/13148 and Appl. Phys. Lett., Vol.58, 18, P 1982, 1991, as well as9,9′,10,10′-tetraphenyl-2,2′-bianthracenes, PPV(polyparaphenylenevinylene) derivatives, polyfluorene derivatives andtheir polymers and others, for example, those having the followingstructures:

and also 9,10-bis(N-(4-(2-phenylvinyl-1-yl)phenyl-N-phenylamino)anthracene, etc. Moreover, phenylanthracene derivatives of the followingformula, such as those described in Japanese Patent Laid-Open No.12600/1996 are also usable for light-emitting materials.

A1—L—A2

wherein A1 and A2 each represent a monophenylanthryl or diphenylanthrylgroup, and these may be the same or different; and L represents a singlebond or a divalent linking group.

Especially preferred are phenylanthracene derivatives of the followinggeneral formulae:

wherein R₁ and R₂ each represent an alkyl group, a cycloalkyl group, anaryl group, an alkenyl group, an alkoxy group, an aryloxy group, anamino group, or a heterocyclic group, and they may be the same ordifferent; r₁ and r₂ each indicate 0 or an integer of from 1 to 5; whenr₁ and r₂ each are an integer of 2 or more, the groups of R₁'s and R₂'seach may be the same or different, and R₁'s and R₂'s may be bonded toeach other to form a ring; L₁ represents a single bond or an arylenegroup, and the arylene group may be interrupted by an alkylene group,—O—, —S— or —NR— (where R indicates an alkyl or aryl group) existingtherein; R₃ and R₄ each represent an alkyl group, a cycloalkyl group, anaryl group, an alkenyl group, an alkoxy group, an aryloxy group, anamino group, or a heterocyclic group, and they may be the same ordifferent; r₃ and r₄ each indicate 0 or an integer of from 1 to 5; whenr₃ and r₄ each are an integer of 2 or more, the groups of R₃'s and R₄'seach may be the same or different, and R₃'s and R₄'s may be bonded toeach other to form a ring; L₂ represents a single bond or an arylenegroup, and the arylene group may be interrupted by an alkylene group,—O—, —S— or —NR— (where R indicates an alkyl or aryl group) existingtherein.

Specific examples of such anthracenes or phenylanthracenes are describedbelow.

In these formulae, R₁₁ to R₄₅ each represent an alkyl group, acycloalkyl group, an aryl group, an alkenyl group, an alkoxy group, anaryloxy group, an amino group, or a heterocyclic group; and they may bethe same or different.

Further mentioned are the following compounds:

Naphthacene derivatives such as those mentioned below are also usablefor light-emitting materials.

wherein X represents a cyano group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted aryl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthio group, a substituted orunsubstituted arylthio group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted heterocyclic group, a substitutedor unsubstituted amino group, or a substituent for rubrene derivatives;i indicates an integer of from 1 to 28; and X's may be the same ordifferent.

Amine compounds such as those mentioned below are also usable forlight-emitting materials.

wherein A¹ to A⁴ each independently represent an aryl group having from6 to 16 carbon atoms; and R¹ to R⁸ each independently represent ahydrogen atom, an alkyl group, an alkoxy group, an aryl group or anamino group.

wherein A and B each represent an optionally-substituted aromatic ring.

wherein A, B, C and D each present a substituted or unsubstituted alkylgroup, a unsubstituted or unsubstituted monocyclic group, or asubstituted or unsubstituted, condensed polycyclic group; and A and B,or C and B may together form a heterocyclic group along with thenitrogen atom that bonds to the skeleton.

Other amine compounds also usable for light-emitting material arementioned below.

wherein A¹ to A⁴ each independently represent an aryl group having from6 to 16 carbon atoms, and the aryl group may be substituted with ahydrogen atom, an alkyl group, an alkoxy group, an aryl group or anamino group; and A represents a single bond, or anoptionally-substituted arylene or polyarylene group.

Aromatic dimethylidene compounds (such as those described in EuropeanPatent 0388768 and Japanese Patent Laid-Open No. 231970/1991) are alsousable for materials for emitting layers. In general, they arerepresented by the following formula:

wherein Ar represents an arylene or polyarylene group; R¹ to R³ eachrepresent a hydrogen atom, an alkyl group or an aryl group; and nindicates an integer of from 1 to 6.

The aryl group includes a phenyl group, a biphenyl group, a terphenylgroup, a naphthyl group, an anthryl group, a phenanthryl group, apyrenyl group, a chrysenyl group, a fluorenyl group, etc. The arylenegroup includes a phenylene group, a biphenylene group, a terphenylenegroup, a naphthylene group, an anthrylene group, a phenanthrylene group,a pyrenylene group, a chrysenylene group, a f luorenylene group, etc.Preferably, the arylene group contains an anthracene skeleton,including, for example, an anthrylene group, a diphenylanthrylene group,a bianthrylene group, etc. R¹ is preferably a hydrogen atom. Specificexamples of the compounds are4,4′-bis(2,2-di-t-butylphenylvinyl)biphenyl,4,4′-bis(2,2-diphenylvinyl)biphenyl,4,4″-bis(2,2-diphenylvinyl)-p-terphenyl,9,10-bis(4′-(2,2-diphenylvinyl)biphenyl)anthracene,9,10-(4-(2,2-diphenylvinyl)phenyl)anthracene,9,9′-(4-(2,2-diphenylvinyl)phenyl)-10,10′-bianthracene, and theirderivatives.

In addition to the above, also usable herein are styryl group-havinglight-emitting materials. For these, preferred are styrylamine compoundsof the following formula:

wherein Ar¹ to Ar⁴ each represent an aryl group, and at least one ofthese is substituted with the following styryl group:

where R¹ to R³ each represent a hydrogen atom, an alkyl group, or anaryl group.

The aryl group for Ar¹ to Ar⁴ and R¹ to R³ includes a phenyl group, abiphenyl group, a terphenyl group, a naphthyl group, an anthryl group, aphenanthryl group, a pyrenyl group, a chrysenyl group, a fluorenylgroup, etc. R¹ is preferably a hydrogen atom. A indicates a linkinggroup, representing a single bond, an arylene group or a polyarylenegroup. It includes a phenylene group, a biphenylene group, an anthrylenegroup, a phenanthrylene group, a pyrenylene group, a chrysenylene group,a diphenylanthrylene group, and also groups having any of the followingstructural formulae:

wherein Ar⁵ and Ar⁶ each represent an aryl group, like Ar¹ to Ar¹.

Also usable herein for light-emitting materials are compounds of ageneral formula, (Rs—Q)₂—Al—O—L wherein L represents a hydrocarbon groupcontaining a phenyl skeleton and having from 6 to 24 carbon atoms; O-Lindicates a phenolato ligand; Q represents a substituted 8-quinolinolatoligand; Rs represents a specifically-selected substituent to be on the8-quinolinolato ring, and it stereospecifically governs the structure ofthe compounds so that more than two substituted 8-quinolinolato ligandsdo not bond to the aluminiumatom. The compounds are described inJapanese Patent Laid-Open No. 258862/1993. Concretely, they includebis(2-methyl-8-quinolinolato) (para-phenylphenolato) aluminium(III),bis(2-methyl-8-quinolinolato)(1-naphtholato)aluminium(III), etc.

In addition to the above, also employable herein is a doping method forefficient mixed emission of blue and green, as in Japanese PatentLaid-Open No. 9953/1994, etc. In the method, the host is any of theabove-mentioned light-emitting materials, and the dopant is afluorescent dye of high blue to green emission. For example, the dopantis a coumarin dye or any other fluorescent dye that may be selected fromfluorescent dyes serving as the host. Concretely, the host is alight-emitting material having a distyrylarylene skeleton, preferably4,4′-bis(2,2-diphenylvinyl)biphenyl, and the dopant is adiphenylaminovinylarylene, preferably N,N-diphenylaminovinylbenzene.

The emitting layer for white emission is not specifically defined, andmay be any of the following:

<1> A layer that defines the energy level of the layers constituting amulti-layered organic EL structure, and emits light through tunnelinjection thereinto (European Patent 0390551);

<2> A layer that emits light through tunnel injection thereinto, like<1> (Japanese Patent Laid-Open No. 230584/1991—its Examples demonstratewhite-emitting devices);

<3> A two-layered emitting layer (Japanese Patent Laid-Open Nos.220390/1990 and 216790/1990);

<4> A layer partitioned into a plurality of sections, in which thelight-emitting materials for the respective sections differ in thewavelength range within which they emit light (Japanese Patent Laid-OpenNo. 51491/1992);

<5> A stacked layer composed of a blue-emitting layer. (having afluorescent peak that falls between 380 and 480 nm) and a green-emittinglayer (having a fluorescent peak that falls between 480 and 580 nm), andfurther containing a red-emitting fluorescent material (Japanese PatentLaid-Open No. 207170/1994);

<6> A combination of a blue-emitting layer that contains a blue-emittingfluorescent dye and a green-emitting layer that contains a red-emittingfluorescent dye, which further contains a green-emitting fluorescentmaterial (Japanese Patent Laid-Open No. 142169/1995).

Of these, especially preferred is the structure <5>.

For the red-emitting fluorescent material, preferred are the followingcompounds:

Next described is a method for forming an emitting layer from any of thematerials mentioned above. Any known methods are applicable to emittinglayer formation, including, for example, vapor deposition, spin coating,LB film formation, etc. For the emitting layer, especially preferred isa molecular deposition film. The molecular deposition film referred toherein is a thin film formed through vapor deposition of a materialcompound of being in a vapor phase condition, or a film formed throughsolidification of a material compound of being in a solution conditionor in a liquid phase condition. In general, the molecular depositionfilm of that type could be differentiated from a thin film (molecularbuilt-up film) formed in a method of LB film formation, because of thedifference therebetween in the aggregation structure and the high-orderstructure and of the functional difference therebetween resulting fromit.

Another method is employable for forming the emitting layer, whichcomprises dissolving a material compound in a solvent along with abinder such as resin or the like to prepare a solution, followed byfilming the resulting solution into a thin film through spin coating orthe like, as in Japanese Patent Laid-Open No. 51781/1982.

The thickness of the emitting layer thus formed in the manner mentionedabove is not specifically defined. Depending on the condition, thethickness of the layer may be suitably varied, but preferably fallsbetween 5 nm and 5 μm. The emitting layer may have a single-layeredstructure comprising one or more of the materials mentioned above, ormay have a multi-layered structure having additional emitting layer(s)of different compound(s).

Next described is the hole injection/transporting layer to be in theorganic EL device of the invention. The layer is to assist holeinjection into the emitting layer, transporting holes to the emittingregion of the emitting layer. Its hole mobility is high, but itsionization energy is small, generally at most 5.5 eV. For the holeinjection/transporting layer, preferred is a material capable oftransporting holes to the emitting layer at a lower field strength. Morepreferably, the hole mobility in the layer is at least 10⁻⁶ cm²/V·sec,for example, in an electric field falling between 10⁴ and 10⁶ V/cm. Thematerial mixed with an aromatic hydrocarbon compound for use herein toform the hole injection/transporting layer is not specifically defined,so far as the layer formed could have the preferred properties mentionedabove. The material for the layer may be selected from any conventionalphotoconductive materials ordinarily used for hole-transportingmaterials, and also from any known materials ordinarily used for holeinjection layers in organic EL devices.

Concretely, the material for forming the hole injection/transportinglayer includes, for example, triazole derivatives (see U.S. Pat. No.3,112,197, etc.), oxadiazole derivatives (see U.S. Pat. No. 3,189,447,etc.), imidazole derivatives (see Japanese Patent Publication No.16096/1962, etc.), polyarylalkane derivatives (see U.S. Pat. Nos.3,615,402, 3,820,989, 3,542,544, Japanese Patent Publication Nos.555/1970, 10983/1976, Japanese Patent Laid-Open Nos. 93224/1976,17105/1980, 4148/1981, 108667/1980, 156953/1980, 36656/1981, etc.),pyrazoline derivatives and pyrazolone derivatives (see U.S. Pat. Nos.3,180,729, 4,278,746, Japanese Patent Laid-Open Nos. 88064/1980,88065/1980, 105537/1974, 51086/1980, 80051/1981, 88141/1981, 45545/1982,112637/1979, 74546/1980, etc.), phenylenediamine derivatives (see U.S.Pat. No. 3,615,404, Japanese Patent Publication Nos. 10105/1976,3712/1971, 25336/1972, Japanese Patent Laid-Open Nos. 53435/1979,110536/1979, 119925/1979, etc.), arylamine derivatives (see U.S. Pat.Nos. 3,567,450, 3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961,4,012,376, Japanese Patent Publication Nos. 35702/1974, 27577/1964,Japanese Patent Laid-Open Nos. 144250/1980, 119132/1981, 22437/1981,German Patent 1,110,518, etc.), amino-substituted chalcone derivatives(see U.S. Pat. No. 3,526,501, etc.), oxazole derivatives (such as thosedescribed in U.S. Pat. No. 3,257,203, etc.), styrylanthracenederivatives (see Japanese Patent Laid-Open No. 46234/1981, etc.),fluorenone derivatives (see Japanese Patent Laid-Open No. 110837/1979,etc.), hydrazone derivatives (see U.S. Pat. No. 3,717,462, JapanesePatent Laid-Open Nos. 59143/1979, 52063/1980, 52064/1980, 46760/1980,85495/1980, 11350/1982, 148749/1982, 311591/1990, etc.), stilbenederivatives (see Japanese Patent Laid-Open Nos. 210363/1986,228451/1986, 14642/1986, 72255/1986, 47646/1987, 36674/1987, 10652/1987,30255/1987, 93455/1985, 94462/1985, 174749/1985, 175052/1985, etc.),silazane derivatives (see U.S. Pat. No. 4,950,950), polysilanederivatives (see Japanese Patent Laid-Open No. 204996/1990),aniline-based copolymers (see Japanese Patent Laid-Open No.282263/1990), electroconductive high-molecular weight oligomers(especially thiophene oligomers) described in Japanese Patent Laid-OpenNo. 211399/1989, etc.

For the materials for the hole injection/transporting layer, usable arethose mentioned above. In addition, also usable are porphyrin compounds(such as those described in Japanese Patent Laid-Open No. 295695/1988,etc.), aromatic tertiary amine compounds and styrylamine compounds (seeU.S. Pat. No. 4,127,412, Japanese Patent Laid-Open Nos. 27033/1978,58445/1979, 149634/1979, 64299/1979, 79450/1980, 144250/1980,119132/1981, 295558/1986, 98353/1986, 295695/1988, etc.), and otheraromatic tertiary amine compounds.

Further usable are compounds having two condensed aromatic rings in themolecule such as those described in U.S. Pat. No. 5,061,569, e.g.,4,4′-bis(N-(1-naphthyl)-N-phenylamino)biphenyl;4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine with threetriphenylamine units being starburst-wise bonded to the center nitrogenatom, such as that described in Japanese Patent Laid-OpenNo.308688/1992, etc. In addition, the aromatic dimethylidene compoundsmentioned hereinabove for the materials for the emitting layer, andinorganic compounds such as p-type Si, p-type SiC and others are alsousable for the materials for the hole injection/transporting layer.

For forming the hole injection/transporting layer, any of the compoundsmentioned above is filmed into a thin film in any known method of, forexample, vacuum evaporation, spin coating, casting, LB film formation,etc. The thickness of the hole injection/transporting layer is notspecifically defined, generally falling between 5 nm and 5 μm. Ifcontaining an aromatic hydrocarbon compound for use herein in its holetransporting zone, the hole injection/transporting layer may have asingle-layered structure comprising one or more of the materialsmentioned above, or may have a multi-layered structure having additionalhole injection/transporting layer(s) of different compound(s).

Next described is the organic semiconductor layer. This is to assisthole injection or electron injection into the emitting layer, andpreferably has en electroconductivity of at least 10⁻¹⁰ S/cm. Examplesof the material for the organic semiconductor layer areelectroconductive oligomers such as thiophene-containing oligomers,arylamine-containing oligomers described in Japanese Patent Laid-OpenNo. 193191/1996, etc.; electroconductive dendrimers such asarylamine-containing dendrimers, etc.

Next described is the electron injection layer. This is to assistelectron injection into the emitting layer, and has high electronmobility. When formed from a material of good adhesion to cathodes, theelectron injection layer serves also as an adhesion improving layer. Forthe materials for the electron injection layer, preferred are metalcomplexes of 8-hydroxyquinoline or its derivatives. Specific examples ofmetal complexes of 8-hydroxyquinoline or its derivatives that serve aselectron-injecting materials for use herein are metal-chelated oxinoidcompounds having an oxine (generally 8-quinolinol or 8-hydroxyquinoline)chelate, such as tris(8-quinolinol)aluminium.

Oxadiazole derivatives that serve as electron-transmitting compounds arealso usable herein. Typically, they are represented by any of thefollowing general formulae [4] to [6]:

wherein Ar¹, Ar², Ar³, Ar⁵, Ar⁶ and Ar⁹ each independently represent asubstituted or unsubstituted aryl group, and these may be the same ordifferent; Ar⁴, Ar⁷ and Ar⁸ each independently represent a substitutedor unsubstituted arylene group, and these may be the same or different.

The aryl group in these formulae [4] to [6] includes a phenyl group, abiphenyl group, an anthranyl group, a perylenyl group, a pyrenyl group.The arylene group therein includes a phenylene group, a naphthylenegroup, a biphenylene group, an anthranylene group, a perylenylene group,a pyrenylene group, etc. The substituents for these groups include analkyl group having from 1 to 10 carbon atoms, an alkoxy group havingfrom 1 to 10 carbon atoms, a cyano group, etc. Of theelectron-transmitting compounds, preferred are those capable of beingreadily filmed into thin films.

Specific examples of the electron-transmitting compounds are mentionedbelow.

Next described is the cathode. For the electrode material for thecathode, usable are metals, alloys, electroconductive compounds andtheir mixtures having a small work function (at most 4 eV). Specificexamples of the electrode material are sodium, sodium-potassium alloys,magnesium, lithium, magnesium-silver alloys, aluminium/aluminium oxide,aluminium-lithium alloys, indium, rare earth metals, etc.

To form the cathode, the electrode material is formed into a thin filmthrough vapor deposition, sputtering or the like.

In case where the light from the emitting layer is taken out through thecathode, it is desirable that the cathode has a light transmittance oflarger than 10%. Also preferably, the sheet resistance of the cathode isat most hundreds Ω/square. The thickness of the cathode generally fallsbetween 10 nm and 1 μm, but preferably between 50 nm and 200 nm.

Next described is a method for fabricating the organic EL device of theinvention. Using the materials mentioned above and according to theprocesses also mentioned above, an anode, an emitting layer, andoptionally a hole injection layer, and further optionally an electroninjection layer are formed in that order, and a cathode is finallyformed. Opposite to this order, a cathode is first formed and an anodeis formed last to finish the organic EL device of the invention.

Described hereinunder is one embodiment of fabricating the organic ELdevice of the invention which has a structure of anode/hole injectionlayer/emitting layer/electron injection layer/cathode formed on atransparent substrate in that order.

A thin film of an anode material having a thickness of at most 1 μm,preferably from 10 to 200 nm is first formed on a suitable transparentsubstrate through vapor deposition or sputtering. This serves as ananode. Next, a hole injection layer is formed on the anode. To form it,employable is any of vacuum evaporation, spin coating, casting, LB filmformation or the like as so mentioned hereinabove, but preferred isvacuum evaporation as ensuring homogeneous films with few pin holes.

In case where the hole injection layer is formed through vacuumevaporation, the condition for vapor deposition varies, depending on thecompound used (for the material for the hole injection layer), and onthe crystal structure and the recombination structure of the holeinjection layer to be formed. In general, it is desirable that thetemperature of the vapor source falls between 50 and 450° C., the vacuumdegree falls between 10⁻⁷ and 10⁻³ Torr, the deposition rate fallsbetween 0.01 and 50 nm/sec; the substrate temperature falls between −50and 300° C., the thickness of the film formed falls between 5 nm and 5μm.

Next, an emitting layer is formed on the hole injection layer. Forforming it, a desired organic light-emitting material is filmed into athin film through vacuum evaporation, sputtering, spin coating, castingor the like. Preferred is vacuum evaporation as ensuring homogeneousfilms with few pin holes. In case where the emitting layer is formedthrough vacuum evaporation, the condition for vapor deposition varies,depending on the compound used. In general, the condition for holeinjection layer formation mentioned above could apply also to theemitting layer formation.

Next, an electron injection layer is formed on the emitting layer. Likethe hole injection layer and the emitting layer, the electron injectionlayer must also be made of a homogeneous film, for which, therefore,preferred is vacuum evaporation. The condition for vapor deposition toform the electron injection layer may also be similar to that to formthe hole injection layer and the emitting layer.

Finally, a cathode is formed on the electron injection layer to finishthe intended organic EL device. The cathode is formed from a metal, forwhich is employable vapor deposition or sputtering. However, in ordernot to damage the underlying organic layers, preferred is vacuumevaporation.

The process of fabricating the organic EL device mentioned above ispreferably achieved in one and the same vacuum chamber in which thedegree of vacuum is not changed throughout the process of forming allthe layers, from the anode to the cathode.

In case where a direct current voltage is applied to the organic ELdevice thus produced in the manner as above, a voltage of from 5 to 40 Vmay be applied thereto with its anode being charged to be plus (+) andits cathode to be minus (−), whereby the device emits light. Even if thesame voltage is applied to the device in the reversed manner relative tothe polarity of the electrodes, the device emits no light. On the otherhand, in case where an alternating current is applied to the device, thedevice emits light only when its anode is charged to be plus (+) and itscathode to be minus (−). The wave mode of the alternating current to beapplied to the device may be any desired one.

In the invention, at least one, but preferably at least two organiccompounds for forming the organic compound layers of the organic ELdevice having the constitution as above have an impurity concentrationof lower than 1000 ppm. In that condition, the organic compounds layersof the device are formed. More preferably, all the organic compoundlayers of the device have an impurity concentration of lower than 1000ppm.

Purification to prepare such high-purity organic compounds is notspecifically defined, and may be effected through sublimation,recrystallization, re-precipitation, zone melting, column purification,adsorption or the like. If desired, these purification methods may becombined in any desired manner. Of those, preferred is recrystallizationfor obtaining the intended high-purity organic compounds. For purifyingsublimable compounds, preferred is sublimation. For purifying sublimablecompounds through sublimation, it is desirable that the sublimation boatis first kept at a temperature lower than the sublimation point of thecompound to be purified so as to previously remove the sublimableimpurities from the compound before the compound is sublimed. Alsopreferably, the zone in which the sublimed compound is collected isdesigned to have a temperature gradient therethrough so that thesublimed mixture could be fractionated into the intended product and theimpurities. The sublimation purification mode mentioned above is forpurifying a compound by removing impurities from it, and is applicableto the invention.

Also preferably, organic compounds in which the oxygen and nitrogenatoms are directly or indirectly bonded to the τ-conjugatedcarbon-carbon main chain (these are referred to as chelate complexcompounds) are purified through sublimation. For sublimationpurification, known are a stirring method and a shaking method. Thestirring method includes (A) a mechanical stirring method in which lumpsof an aggregated organic compound are directly crushed and milled with aman-powered or machine-powered stirring blade fitted to the tip of astirrer sealed in vacuum, and stirring the system is continued so thatthe milled power is prevented from again aggregating to form lumps; (B)a magnetic stirring method in which is used a magnetic bar for millingan organic compound to be purified through sublimation in such a mannerthat the magnetic bar is rotated at a desired speed of rotation by theuse of an external rotating machine to thereby directly crush and millthe lumps of the organic compound, and stirring the system is continuedso that the milled power is prevented from again aggregating to formlumps; and (C) a method of dropping metal balls such as iron balls orthe like onto the lumps of an organic compound to thereby directly crushand mill the lumps. Any of these methods is employable herein.

The shaking method includes (a) an ultrasonic shaking method in which anorganic compound to be purified through sublimation is put into acontainer and exposed to ultrasonic waves from an external ultrasonicwave generator, thereby crushing and milling the lumps of the organiccompound; and (b) a direct shaking method in which an organic compoundto be purified through sublimation is put into a container, and thecontainer is directly shaken by an external shaking machine fitted tothe container or by human power applied thereto to thereby crush andmill the lumps of the organic compound. Any of these methods isemployable herein.

The organic compound of which the impurity content has been reduced tosmaller than 1000 ppm in the manner mentioned above is used for formingat least one organic compound layer of the organic EL device of theinvention.

The impurities that may be in the organic compound materials to beformed into the organic compound layers of the device of the inventionare generally derived from the starting substances used for preparingthe organic compound materials, further including intermediates andprecursors produced in the process of preparing the organic compounds(some intermediates and precursors produced in the process often have areactive functional group). In addition, in case where halogen compoundsare used in the process of preparing the organic compounds, unreactedintermediates will remain in the reaction system, and the startinghalogen compounds not reacted completely will also remain therein. Theseunreacted intermediates and halogen compounds will be impurities in theorganic compounds prepared. Moreover, in case where halogen solvents areused in the process of preparing the organic compounds, the organiccompounds prepared will be often contaminated by halogen (e.g.,chlorine)-added olefins, or, depending on the reaction condition, byoxidized organic compounds.

Accordingly, the organic compound materials are, immediately afterhaving been prepared through chemical synthesis, often contaminated byimpurities of various compounds. Of all such impurities, we, the presentinventors have found that halogen compounds are the most serious, assignificantly attenuating emission luminance and shortening the emissionlife. Many impurities mentioned above contain halogen atoms acting as areactive functional group, and they trap holes and electrons that havemoved from the electrodes into the organic compound layers. Accordingly,the acceptable uppermost limit of the halogen-containing impurities thatmay be in the organic compound materials is 500 ppm. We have found thatorganic EL devices in which the organic compound layers are formed frommaterials having a halogen compound content higher than the uppermostlimit are often significantly confronted with the problems of emissionluminance attenuation and short emission life.

Just after having been prepared through chemical synthesis, organiccompound materials are often contaminated with impurities, which aredescribed more concretely. For example, in chemical synthesis ofproducing styryl compounds to be represented by the following reactionformula:

wherein Ar, Ar′, X and Y each represent an aryl group; and

Z represents a halogen atom,

halogen compounds of the following formulae:

wherein Ar, Ar′, X and Y each represent an aryl group; and

Z represents a halogen atom.

exist as impurities in the reaction system. Accordingly, organiccompound materials comprising the styryl compounds prepared through thereaction mentioned above are contaminated with the impurities of suchhalogen compounds.

In chemical synthesis of producing amine compounds to be represented bythe following reaction formula:

wherein Ar, Ar′ and Ar″ each represent an aryl group; and

Z represents a halogen atom,

halogen compounds of the following formulae:

wherein Ar, Ar′ and Ar″ each represent an aryl group; and

Z represents a halogen atom,

and also amine oxides exist as impurities in the reaction system.Accordingly, organic compound materials comprising the amine compoundsprepared through the reaction mentioned above are contaminated with theimpurities of such halogen compounds and amine oxides. These areexamples of intermediates and precursors in the process of chemicalsynthesis.

Amine compounds may be prepared through the following reaction, whichalso gives some impurities to be mentioned below.

In these processes, the products produced will be contaminated with thefollowing impurities, intermediates or precursors.

wherein Ar, Ar′ and Ar″ each represent an aryl group; and Z represents ahalogen atom.

Polyfluorenone compounds will be contaminated with the followingimpurities:

wherein Z represents a halogen atom.

In case where various organic compounds for use herein are produced inother processes of chemical reaction, the organic compounds producedshould be so controlled that their impurity content is smaller than 1000ppm, including 0 ppm. The impurities of the organic compounds may bederived from the starting substances used, or may be intermediates orprecursors formed in the process of chemical reaction to give theorganic compounds, or may be such intermediates or precursors having areactive functional group (including, for example, halogens, amino,hydroxy and carboxyl groups, etc.).

Various methods are known for quantifying the impurity content of theorganic compound materials purified in various purification methods suchas those mentioned above. In the invention, the purified organiccompound materials are analyzed through high-performance liquidchromatography to quantify the impurities therein, and those of whichthe impurity content is lower than the predetermined value as above areselectively used for forming the organic compound layers of the organicEL device of the invention. For selecting the organic compound materialsfor use herein, high-performance liquid chromatographyis preferred toany other methods. This is because organic compound materials suitableto the invention are selected more rapidly and more accurately in themethod of high-performance liquid chromatography than in any othermethods.

In the method of high-performance liquid chromatography, the mobilephase is moved in the column by the power of a high-pressure pump(pressure: 350 to 500 kg/cm²). In the method, therefore, the time forseparation is short, and rapid quantification is possible. The fillerfor the method comprises porous particles all having a small grain sizeof from 5 to 10μ and having a large surface area, and therefore has goodseparation capability. The column can be connected with ahigh-sensitivity detector, in which accurate analysis is possible. Inaddition, since the flow rate through the column can be kept constantall the time, the method of high-performance liquid chromatographyensures good reproducibility. Some typical examples of the filler andthe separation mode for the method of high-performance liquidchromatography are shown in Table 1.

TABLE 1 Parameter for Separation Mode Separation Typical FillerPartitioning Solubility Chemical-bonding silica gel, ChromatographyPolymer gel, Carbon, Chemical-bonding porous glass AdsorptionAdsorbability Silica gel, Alumina, Chromatography Porous glass, CarbonIon-exchange Ion-exchangeability Ion-exchangeable Chromatographypolystyrene gel, Ion-exchangeable chemical-bonding silica gel,Ion-exchangeable hydrophilic polymer gel Sizing Molecular sizePolystyrene gel, Chromatography Hydrophilic polymer gel,Chemical-bonding silica gel Affinity Biochemical affinity Ligand-bondingChromatography hydrophilic polymer, Ligand-bonding silica gel

In the method of high-performance liquid chromatography, the separationmode varies, depending on the fixed phase and the mobile phase, and maybe any desired one.

For quantifying the impurities in the organic compound materials to beused herein for forming organic compound layers of the organic EL deviceof the invention, preferred is reversed-phase chromatography as itsseparation efficiency is good. Reversed-phase chromatography is a typeof partitioning chromatography, and the filler used therein is ODS(octadecyl-bonding silica) which is a type of chemical-bonding silicagel. Such an ODS filler is a typical one for high-performance liquidchromatography, and is applicable to a broad range of various compounds.The solvent for reversed-phase chromatography may be a polar solventincluding methanol, acetonitrile and others, or may also be a mixedsolvent of water and such a polar solvent. Especially preferred isacetonitrile.

Any detector is usable in high-performance liquid chromatography,including, for example, an ultraviolet absorptiometer (UV), adifferential refractometer (RI), etc. Preferred is an ultravioletabsorptiometer (w), since the base line for the data detected therein isstable, and the data are not influenced by the ambient temperature andthe flow rate, therefore ensuring high-sensitivity detection.

Accordingly, the best combination of the filler, the solvent and thedetector for high-performance liquid chromatography to be employedherein is as follows. The filler is ODS; the solvent is acetonitrile forreversed-phase chromatography; and the detector is an ultravioletabsorptiometer (UV).

In case where the organic compound materials to be used for forming thelayers of the organic EL device of the invention are soluble in thesolvent, acetonitrile, there occurs no problem in analyzing thematerials through high-performance liquid chromatography with thesolvent, acetonitrile. However, in case where the materials are hardlysoluble in the solvent, acetonitrile, they must be processed as follows:The material to be analyzed is first dissolved in a solvent capable ofdissolving it, and then a bad solvent, for example, methanol or a mixedsolvent of methanol and water is added to the resulting solution forre-precipitating it. Next, the insoluble solid is taken out throughfiltration, and the solvent is completely evaporated away by the use ofan evaporator. Acetonitrile is added to this to prepare a samplesolution of the material in acetonitrile. In that manner, the organiccompound materials hardly soluble in acetonitrile can be analyzedthrough high-performance liquid chromatography with acetonitrile.

Next, the invention is described in more detail with reference to thefollowing Examples.

PRODUCTION EXAMPLE 1 Preparation of Hole Injection Material

4,4′,4″-Tris-[N-(M-tolyl)-N-phenylamino]triphenylamine (hereinafterreferred to as MTDATA) having the following formula is prepared in themanner mentioned below. This serves as a hole injection material.

1.0 g of 4,4′,4″-triiodotriphenylamine, 1.0 g ofN-(3-tolyl)-N-phenylamine (from Aldrich), 3 g of anhydrous potassiumcarbonate and 1.0 g of copper powder were put into a 300-ml three-neckflask, to which was added 200 ml of dimethylsulfoxide to dissolve them.At 200° C., these were reacted for 8 hours with stirring. After havingbeen reacted, the reaction mixture was filtered, and the mother filtratewas extracted with methylene chloride. Next, the solvent was evaporatedaway by the use of a rotary evaporator. The residue was subjected tocolumn chromatography, for which the column was filled with silica geland the developer was toluene. 0.3 g of a pale yellow powder wasobtained. This is hereinafter referred to as impure MTDATA.

The impure MTDATA was analyzed through high-performance liquidchromatography. The impurities detected were N-(3-tolyl)-N-phenylamine,halogen-containing impurities such as triiodotriphenylamine derivatives,diiodotriphenylamine derivatives, monoiodotriphenylamine derivatives,and amine oxides. The amount of some these impurities fell between 1000and 10000 ppm.

Next, the impure MTDATA was purified through sublimation to remove theimpurities from it. The boat temperature was 390° C., and the vacuumdegree was 10⁻⁶ Torr. As a result, obtained was 0.24 g of a pale yellowpowder. This is hereinafter referred to as sublimed MTDATA. The sublimedMTDATA was analyzed through high-performance liquid chromatography,which confirmed that the amount of the above-mentioned impurities wasall smaller than 1000 ppm.

PRODUCTION EXAMPLE 2 Preparation of Hole Transporting Material

N,N′-Di(naphthyl-1-yl)-N,N′-diphenyl-4,4′-benzidine (hereinafterreferred to as NPD) having the following formula is prepared in themanner mentioned below. This serves as a hole transporting material.

2.0 g of 1-iodonaphthalene (from Tokyo Chemical), 1.0 g ofN,N′-diphenylbenzidine (from Aldrich), 3 g of anhydrous potassiumcarbonate and 1.0 g of copper powder were put into a 300-ml three-neckflask, to which was added 200 ml of dimethylsulfoxide to dissolve them.At 200° C., these were reacted for 8 hours with stirring. After havingbeen reacted, the reaction mixture was filtered, and the mother filtratewas extracted with methylene chloride. Next, the solvent was evaporatedaway by the use of a rotary evaporator. The residue was subjected tocolumn chromatography, for which the column was filled with silica geland the developer was toluene. 0.37 g of a pale yellow powder wasobtained. This is hereinafter referred to as impure NPD.

The impure NPD was analyzed through high-performance liquidchromatography. The impurities detected were the halogen-containingnon-reacted compound, 1-iodonaphthalene, and alsoN-(naphthyl-1-yl)-N,N′-diphenyl-4,4′-benzidine, and amine oxides. Theamount of some these impurities fell between 1000 and 10000 ppm.

Next, the impure NPD was purified through sublimation to remove theimpurities from it. The boat temperature was 320° C., and the vacuumdegree was 10⁻⁶ Torr. As a result, obtained was 0.31 g of a pale yellowpowder. This is hereinafter referred to as sublimed NPD. The sublimedNPD was analyzed through high-performance liquid chromatography, whichconfirmed that the amount of the above-mentioned impurities was allsmaller than 1000 ppm.

PRODUCTION EXAMPLE 3 Preparation of Dopant

4,4′-Bis[2-{4-(N,N-diphenylamino)phenyl}vinyl]biphenyl (hereinafterreferred to as DPAVBi) having the following formula is prepared in themanner mentioned below. This serves as a dopant.

1.9 g of biphenyl phosphonate and 3.0 g ofN,N-diphenyl-4-aminobenzaldehyde were put into a 200-ml three-neckflask, to which was added 50 ml of dimethylsulfoxide to dissolve them.Next, with stirring them in an argon atmosphere at room temperature witha magnetic stirrer, 1.0 g of powdery potassium t-butoxide (from KantoChemical) was added thereto little by little. The reaction mixtureimmediately became reddish black, and then faded to give a precipitatewhich was first greenish yellow and then ocher. The reaction mixture wasfurther stirred at room temperature for 3 hours. This was left at roomtemperature overnight, and then 50 ml of aqueous 80 wt. % methanolsolution was gradually added thereto. Then, the yellow precipitateformed was taken out through filtration, and then washed with water.Washing it was repeated a few times. An yellow powder was obtained,weighing 2.8 g.

The thus-obtained yellow powder was purified through silica gel columnchromatography, for which the developer was toluene, and thenrecrystallized from toluene. Recrystallizing it was repeated a fewtimes. An yellow powder was obtained, weighing 1.6 g.

The product thus obtained was analyzed through high-performance liquidchromatography. The impurities detected were4-(N,N-diphenyl)-4′-(p-tolyl)stilbene and amine oxides, but were allsmaller than 1000 ppm.

PRODUCTION EXAMPLE 4 Preparation of Light-emitting Material

4,4″-Bis(2,2-diphenylvinyl)-p-terphenyl (hereinafter referred to asDPVTP) having the following formula is prepared in the manner mentionedbelow. This serves as a light-emitting material.

200 g of diphenylbromomethane and 146 g of triethyl phosphite werestirred under heat at 120 to 130° C. for 8 hours. After reacted, thiswas cooled and decanted with 500 ml of n-hexane. The solvent wasevaporated away, and 284 g of an yellow liquid was obtained. Next, 284 gof the resulting phosphonate and 182 g of p-bromobenzaldehyde weredissolved in 1 liter of dimethylsulfoxide. 113 g of potassium t-butoxidewas divided into a few portions, and intermittently added to thesolution at room temperature. Next, this was stirred at room temperaturefor 8 hours, and the reaction mixture was poured into 3.5 liters ofwater and then extracted three times with 1 liter of chloroform. Thiswas further purified through silica gel column chromatography, and 206 g(yield: 62%) of a white powder was obtained. 20 g of the bromide wasdissolved in 50 ml of anhydrous tetrahydrofuran (from Wako PureChemicals), and the resulting solution was dropwise added to 65 ml oftetrahydrofuran containing 1.2 g of magnesium, at 50 to 60° C. After theaddition, the reaction mixture was refluxed for 1 hour. Thus wasprepared a Grignard reagent.

Next, 4.0 g of 1,4-dibromobenzene, 0.6 g of bistriphenylphosphinepalladium, 1.8 ml of hydrogenated diisobutylaluminium hydride, and 200ml of tetrahydrofuran were put into a 300-ml three-neck flask. Withkeeping the mixture at 50 to 60° C. in an argon atmosphere, the Grignardreagent having been prepared previously was dropwise added thereto overa period of 30 minutes. After the addition, the reaction mixture wasstirred for 8 hours. Next, this was left cooled, and then poured into anaqueous 3 N HCl solution. The precipitate thus formed was washed withwater, dried, and then purified through silica gel columnchromatography, for which the developer was methylene chloride. A whitepowder was thus obtained, weighing 3.0 g. This is hereinafter referredto as impure DPVTP.

The impure DPVTP was analyzed through high-performance liquidchromatography. The impurities detected were halogen-containingimpurities from the starting compounds, such asdiphenylvinylbromobenzene, and halogen-containing impurities(intermediates) having been semireacted, such asdiphenylvinyl-p-bromobiphenyl. The amount of some these impurities fellbetween 1000 and 10000 ppm.

Next, the impure DPVTP was purified through sublimation to remove theimpurities from it. The boat temperature was 330° C., and the vacuumdegree was 10⁻⁶ Torr. As a result, obtained was 2.0 g of a pale yellowmilky powder. This is hereinafter referred to as sublimed DPVTP. Thesublimed DPVTP was analyzed through high-performance liquidchromatography, which confirmed that the amount of the above-mentionedimpurities was all smaller than 1000 ppm.

PRODUCTION EXAMPLE 5 Preparation of Light-emitting Material

9,10-Bis(4-(2,2-diphenylvinyl)phenyl)anthracene (hereinafter referred toas DPVDPAN) is prepared according to the following reaction scheme. Thisserves as a light-emitting material.

200 g (0.8 mols) of diphenylbromomethane and 146 g (1 mol) of triethylphosphite were stirred under heat at 120 to 130° C. for 8 hours. Afterreacted, this was cooled and decanted with 500 ml of n-hexane. Thesolvent was evaporated away, and 284 g of an yellow liquid was obtained.Next, 284 g of the resulting phosphonate and 182 g (0.9 mols) ofp-bromobenzaldehyde were dissolved in 1 liter of dimethylsulfoxide. 113g of potassium t-butoxide was divided into a few portions, andintermittently added to the solution at room temperature. Next, this wasstirred at room temperature for 8 hours, and the reaction mixture waspoured into 3.5 liters of water and then extracted three times with 1liter of chloroform. This was further purified through silica gel columnchromatography, and 206 g (yield: 62%) of a white powder was obtained.

Next, 1/5 of a solution of 149.7 g (446.39 mmols,×3.0 eq) of thecompound [A] in 1000 ml of tetrahydrofuran was first added to adispersion of 16.3 g (669.58 mmols,×4.5 eq) of magnesium in 500 ml oftetrahydrofuran, in an argon stream atmosphere, and heated at 50 to 60°C. Then, the remaining solution was dropwise added thereto over a periodof 1 hour. After the addition, this was reacted at 60 to 65° C. for 5hours (<1>).

Apart from the reaction <1>, 4.2 g (5.95 mmols, ×0.04 eq) ofPdCl₂(PPh₃)₂ was added to a solution of 50.5 g (148.80 mmols) of9,10-dibromoanthracene [B] in 1000 ml of tetrahydrofuran, in an argonstream atmosphere, and then 14.9 ml (14.88 mmols, ×0.1 eq) ofisobutylaluminium hydride (in toluene, 1.0 mol/liter) was added thereto.Next, this was reacted at 50 to 55° C. for 4 hours, and the reactionmixture <1> was dropwise added thereto over a period of 20 minutes.After the addition, this was reacted at 65° C. for 18 hours (<2>).

At about 60° C., the reaction mixture was filtered under reducedpressure, and washed with 500 ml of tetrahydrofuran and then twice with100 ml of acetone in that order. The crystal thus taken out throughfiltration was dissolved in 14000 ml of dimethylsulfoxide under heat,and recrystallized therein. Thus was obtained a yellowish milky crystal.It weighed 71.0 g, and its yield was 68.7%.

The impure DPVDPAN was analyzed through high-performance liquidchromatography. The impurities detected were halogen-containingintermediates, such as the compound [A] and a semireacted compound ofthe following formula:

The amount of some these impurities fell between 10000 and 20000 ppm.

Next, the impure DPVDPAN was purified through sublimation to remove theimpurities from it. The boat temperature was 380° C., and the vacuumdegree was 10⁻⁶ Torr. As a result, obtained was a pale yellow milkypowder. This is hereinafter referred to as sublimed DPVDPAN. Thesublimed DPVDPAN was analyzed through high-performance liquidchromatography, which confirmed that the amount of the above-mentionedimpurities was all smaller than 500 ppm.

EXAMPLE 1

A film electrode of ITO (indium-tin oxide) having a thickness of 100 nmwas formed on a glass sheet having a size of 25 mm×75 mm×1.1 mm toprepare a transparent substrate. The substrate was ultrasonically washedwith isopropyl alcohol for 5 minutes, then washed with water for 5minutes, and finally again ultrasonically washed with isopropyl alcoholfor 5 minutes. Next, the thus-washed transparent substrate was fixed ona substrate holder in a vacuum evaporation apparatus (by Nippon VacuumTechnology). This vapor deposition apparatus was equipped with aplurality of independent resistance-heating boats of molybdenum, intowhich were put vaporizing organic compounds. Precisely, 200 mg of thesublimed MTDATA serving as a hole injection material; 200 mg of thesublimed NPD serving as a hole transporting material; 200 mg of thesublimed DPVTP serving as a light-emitting material; 200 mg of DPAVBiserving as a dopant; and 200 mg of the followingtris(8-hydroxyquinolinol) (hereinafter referred to as ALQ) serving as anelectron transporting material were separately put into those boats.

Next, the vacuum chamber of the apparatus was degassed to have a vacuumdegree of 1×10⁻⁶ Torr, and the boat with MTDATA being put therein waselectrically heated up to 360° C. so that the compound in the boat wasvaporized and deposited onto the transparent substrate at a depositionrate of from 0.1 to 0.3 nm/sec to form a hole injection layer of MTDATAhaving a thickness of 60 nm.

Next, the boat with NPD being put therein was electrically heated up to260° C. so that the compound in the boat was vaporized and depositedover the hole injection layer of MTDATA at a deposition rate of from 0.1to 0.3 nm/sec to form thereon a hole transporting layer of NPD having athickness of 20 nm.

Next, the boat with DPVTP being put therein and the boat with DPAVBibeing put therein were electrically heated at the same time to form amixed emitting layer of DPVTP and DPAVBi having a thickness of 40 nm, inwhich the ratio of DPVTP/DPAVBi was 40/1 by weight.

Next, the thus-layered substrate was taken out of the vacuum chamber,then provided with a stainless steel mask, and thereafter again fixed onthe substrate holder. Next, a cathode-forming, vaporizing material of analuminium-lithium (Al—Li) alloy having a lithium content of 5 atomic %was vaporized and deposited on the substrate at a deposition rate offrom 0.5 to 1.0 nm/sec to form thereon a cathode film having a thicknessof 150 nm. During the deposition, the vacuum degree in the chamber was1×10⁻⁶ Torr.

The thus-fabricated, organic EL device was tested for light emissionwith 6 V current being applied thereto between the ITO anode and theAl—Li alloy cathode of the device, whereupon the device emitted uniformblue light. The initial data of the device thus driven at 6 V were asfollows: The current density was 1.2 mA/cm2, the luminance was 100cd/m², and the emission efficiency was 4.2 lumens/W. With its initialluminance being 100 cd/m², the device was driven at a constant currentin a nitrogen atmosphere. In that condition, the half lifetime of thedevice, within which the luminance thereof was attenuated to 50 cd/m²,was longer than 5000 hours.

The constitution and the half lifetime of the organic EL device aregiven in Table 2.

EXAMPLES 2 TO 7

Partly different organic EL devices were fabricated and evaluated in thesame manner as in Example 1, for which, however, the organic compoundshaving been prepared in the above-mentioned Production Examples werecombined as in Table 2.

The constitution and the half lifetime of the organic EL devices aregiven in Table 2.

TABLE 2 Hole Hole Light- Electron Injection Transporting emittingTransporting Half Lifetime (hrs) Material Material Dopant MaterialMaterial with initial luminance Example (MTDATA) (NPD) (DPAVBi) (DPVTP)(ALQ) of 100 cd/m² 1 sublimed sublimed pure sublimed pure 7000 2sublimed sublimed pure impure pure 5000 3 sublimed impure pure sublimedpure 6000 4 impure sublimed pure sublimed pure 4000 5 impure impure puresublimed pure 3500 6 impure sublimed pure impure pure 3500 7 sublimedimpure pure impure pure 3000

INDUSTRIAL APPLICABILITY

The organic EL device of the invention has the advantages ofapplicability to lightweight, thin and low-voltage driving displays,good luminescent capacity attenuating little even in long-term drivingoperation, and good durability.

What is claimed is:
 1. An organic electroluminescent device thatcomprises organic compound layer(s) including at least one organicemitting layer sandwiched between a pair of electrodes, wherein at leastone organic compound layer is formed from an organic compound materialhaving an impurity concentration of lower than 1000 ppm, and whereinsaid organic emitting layer comprises at least one light emittingmaterial selected from the group consisting of (a), (b), (c), (d), (e),(f) and combinations thereof:

wherein in (a), R₁ and R₂ may be the same or different and eachindependently represents an alkyl group, a cycloalkyl group, an arylgroup, an alkenyl group, an alkoxy group, an aryloxy group, an aminogroup, or a heterocyclic group; r₁ and r₂ each is 0 or an integer offrom 1 to 5; wherein when r₁ and r₂ each are an integer of 2 or more,the groups of R₁'s and R₂'s each may be the same or different, and R₁'sand R₂'s may be bonded to each other to form a ring; L₁ represents asingle bond or an arylene group, and the arylene group may beinterrupted by an alkylene group, —O—, —S— or —NR—, wherein R is analkyl or aryl group; wherein in (b), R₃ and R₄ may be the same ordifferent, and each independently represents an alkyl group, acycloalkyl group, an aryl group, an alkenyl group, an alkoxy group, anaryloxy group, an amino group, or a heterocyclic group; r₃ and r₄ eachis 0 or an integer of from 1 to 5; wherein when r₃ and r₄ each are aninteger of 2 or more, the groups of R₃'s and R₄'s each may be the sameor different, and R₃'s and R₄'s may be bonded to each other to form aring; L₂ represents a single bond or an arylene group, and the arylenegroup may be interrupted by an alkylene group, —O—, —S— or —NR—, whereinR indicates an alkyl or aryl group; wherein in (c), A¹ to A⁴ eachindependently represent an aryl group having from 6 to 16 carbon atoms,which aryl group may be substituted with a hydrogen atom, an alkylgroup, an alkoxy group, an aryl group or an amino group; and Arepresents a single bond or an optionally-substituted arylene orpolyarylene group; wherein in (d), Ar represents an arylene orpolyarylene group; R¹ to R³ each represent a hydrogen atom, an alkylgroup or an aryl group; and n is an integer of from 1 to 6; wherein in(e), Ar¹ to Ar⁴ each represent an aryl group, at least one of which issubstituted with the following group:

wherein R1 to R3 each represent a hydrogen atom, an alkyl group, or anaryl group; and wherein in (f), Ar′, Ar″, X and Y each represent an arylgroup.
 2. An organic electroluminescent device that comprises organiccompound layer(s) including at least one organic emitting layersandwiched between a pair of electrodes, wherein at least one organiccompound layer is formed from an organic compound material having animpurity concentration of lower than 500 ppm and the impurity therein isa halogen containing compound, and wherein said organic emitting layercomprises at least one light emitting material selected from the groupconsisting of (a), (b), (c), (d), (e), (f) and combinations thereof:

wherein in (a), R₁ and R₂ may be the same or different and eachindependently represents an alkyl group, a cycloalkyl group, an arylgroup, an alkenyl group, an alkoxy group, an aryloxy group, an aminogroup, or a heterocyclic group; r₁ and r₂ each is 0 or an integer offrom 1 to 5; wherein when r₁ and r₂ each are an integer of 2 or more,the groups of R₁'s and R₂'s each may be the same or different, and R₁'sand R₂'s may be bonded to each other to form a ring; L₁ represents asingle bond or an arylene group, and the arylene group may beinterrupted by an alkylene group, —O—, —S— or —NR—, wherein R is analkyl or aryl group; wherein in (b), R₃ and R₄ may be the same ordifferent, and each independently represents an alkyl group, acycloalkyl group, an aryl group, an alkenyl group, an alkoxy group, anaryloxy group, an amino group, or a heterocyclic group; r₃ and r₄ eachis 0 or an integer of from 1 to 5; wherein when r₃ and r₄ each are aninteger of 2 or more, the groups of R₃'s and R₄'s each may be the sameor different, and R₃'s and R₄'s may be bonded to each other to form aring; L₂ represents a single bond or an arylene group, and the arylenegroup may be interrupted by an alkylene group, —O—, —S— or —NR—, whereinR indicates an alkyl or aryl group; wherein in (c), A¹ to A⁴ eachindependently represent an aryl group having from 6 to 16 carbon atoms,which aryl group may be substituted with a hydrogen atom, an alkylgroup, an alkoxy group, an aryl group or an amino group; and Arepresents a single bond or an optionally-substituted arylene orpolyarylene group; wherein in (d), Ar represents an arylene orpolyarylene group; R¹ to R³ each represent a hydrogen atom, an alkylgroup or an aryl group; and n is an integer of from 1 to 6; wherein in(e), Ar¹ to Ar⁴ each represent an aryl group, at least one of which issubstituted with the following group:

wherein R¹ to R³ each represent a hydrogen atom, an alkyl group, or anaryl group; and wherein in (f), Ar′, Ar″, X and Y each represent an arylgroup.
 3. The organic electroluminescent device as claimed in claim 2,wherein the halogen-containing compound is a halide.
 4. The organicelectroluminescent device as claimed in claim 1, wherein the organiccompound layers are a hole injection layer, an organic emitting layerand an electron injection layer.
 5. The organic electroluminescentdevice as claimed in claim 1, wherein at least one organic compoundmaterial to form the organic compound layer(s) is purified throughsublimation.
 6. The organic electroluminescent device as claimed inclaim 1, wherein at least one organic compound material to form theorganic compound layer(s) is purified through recrystallization orreprecipitation, or through recrystallization combined withreprecipitation.
 7. A method for selecting organic compound materialsfor organic electroluminescent devices, comprising determining, throughhigh-performance liquid chromatography, the impurity content of eachorganic compound material to form organic compound layers for thedevices, selecting those having an impurity content of smaller than 1000ppm out of the materials analyzed, and using the thus-selected materialsfor forming the organic compound layers.
 8. A method for selectingorganic compound materials for organic electroluminescent devices,comprising determining the impurity content of at least one organiccompound material to form organic compound layers for the devices,selecting those having an impurity content of smaller than 1000 ppm outof the materials analyzed, and using the thus-selected materials forforming the organic compound layers.
 9. The method as claimed in claim 7for selecting organic compound materials for organic electroluminescentdevices, wherein the impurity in the organic compound materials is ahalogen-containing compound.
 10. The method as claimed in claim 8 forselecting organic compound materials for organic electroluminescentdevices, wherein the impurity in the organic compound materials is ahalogen-containing compound.
 11. The organic electroluminescent deviceas claimed in claim 2, wherein the halogen-containing compound comprisesa halide selected from the group consisting of chloride, iodide, andbromide.
 12. The organic electroluminescent device as claimed in claim1, wherein the impurity is at least one compound comprising a halideselected from the group consisting of chloride , iodide, and bromide.13. The method as claimed in claim 7, wherein the impurity is at leastone compound comprising a halide selected from the group consisting ofchloride, iodide, and bromide.
 14. The method as claimed in claim 8,wherein the impurity is at least one compound comprising a halideselected from the group consisting of chloride, iodide, and bromide. 15.The organic electroluminescent device as claimed in claim 1, wherein theorganic compound layer comprises said organic compound material, andsaid organic compound material has an impurity concentration of lessthan 1000 ppm.
 16. The organic electroluminescent device as claimed inclaim 1, wherein the organic compound layer comprises said organiccompound material, and said organic compound material has an impurityconcentration of less than 500 ppm.
 17. The organic electroluminescentdevice as claimed in claim 1, wherein the organic compound layercomprises said organic compound material, and said organic compoundmaterial has an impurity concentration of 0 ppm.
 18. The organicelectroluminescent device as claimed in claim 1, wherein the organiccompound layer comprises said organic compound material, and saidorganic compound material has an impurity concentration of less than1000 ppm, and said impurity is at least one compound selected from thegroup consisting of an amine oxide, chloride-containing compound,iodide-containing compound, bromide-containing compound, oxidizedorganic compound, amino-containing compound, hydroxy-containingcompound, and carboxyl-containing compound.
 19. The method as claimed inclaim 7, wherein the impurity is at least one compound selected from thegroup consisting of an amine oxide, chloride-containing compound,iodide-containing compound, bromide-containing compound, oxidizedorganic compound, amino-containing compound, hydroxy-containingcompound, and carboxyl-containing compound.
 20. The method as claimed inclaim 8, wherein the impurity is at least one compound selected from thegroup consisting of an amine oxide, chloride-containing compound,iodide-containing compound, bromide-containing compound, oxidizedorganic compound, amino-containing compound, hydroxy-containingcompound, and carboxyl-containing compound.
 21. The organicelectroluminescent device as claimed in claim 1, wherein the lightemitting material is (a).
 22. The organic electroluminescent device asclaimed in claim 1, wherein the light emitting material is (b).
 23. Theorganic electroluminescent device as claimed in claim 1, wherein thelight emitting material is (c).
 24. The organic electroluminescentdevice as claimed in claim 1, wherein the light emitting material is(d).
 25. The organic electroluminescent device as claimed in claim 1,wherein the light emitting material is (e).
 26. The organicelectroluminescent device as claimed in claim 1, wherein the lightemitting material is (f).
 27. The organic electroluminescent device asclaimed in claim 2, wherein the light emitting material is (a).
 28. Theorganic electroluminescent device as claimed in claim 2, wherein thelight emitting material is (b).
 29. The organic electroluminescentdevice as claimed in claim 2, wherein the light emitting material is(c).
 30. The organic electroluminescent device as claimed in claim 2,wherein the light emitting material is (d).
 31. The organicelectroluminescent device as claimed in claim 2, wherein the lightemitting material is (e).
 32. The organic electroluminescent device asclaimed in claim 2, wherein the light emitting material is (f).